Monthly Archives: January 2007

Ofcom Prosecution Statistics

For those readers who live outside the UK, the government department responsible for policing the radio spectrum is called Ofcom.  Ofcom has recently published its 2005/2006 prosecution statistics. This shows that their resources almost exclusively spent their time shutting down unlicenced broadcast stations (that operate on the 88 to 108Mhz FM band I suppose) and unlicensed Private Business Radio operators.

Out of 52 prosecutions, they secured 52 convictions. A case of making sure you have very strong evidence I assume. However only 4 warning letters were sent out to the hobby market; these four letters covered all those 27Mhz stations running 500 watts, those ops on 6.6Mhz and all those radio amateurs broadcasting music on repeaters (eg GB3 Charlie Fox middle of January 2007) and generally causing a mess of QRM. Not a single prosecution.

Looks like you can get away with murder then? 

Yaesu FT1000MP Mk-5 IDBT controls

I’ve just found this page on the internet whilst I was doing a search to track down exactly how the IDBT control works on my Yaesu FT1000MP Mark IV (Mk 5). It stands for something like Interlocked Digital (analog) Bandwidth Tracking and it’s part of the EDSP controls. Thierry explains it better than me, however I’m a happy bunny now because I can get the Mk5 sounding like my original MP 🙂

Anyway, these deeper (advanced..?) instructions beat the instruction manual hands down. Merci Thierry!

Shortened / loaded 40 meter dipole for attics

This morning, I removed from the loft, a pair of nested dipoles for 40 and 20 meters fed with one coax feeder. The 40 meter dipole was loaded with some coils so that I could fit it in the attic.

It gave me 40, 20 and 15 with a push because although a 40 meter dipole should give you a resonant 15 meter antenna, in this case – with the coils for 40 – it mucked the maths up and caused the ATU some trouble. On 40m, it worked a treat.

If anyone is interested in making up the “shorty forty”, you may find my experience of interest: Each coil was made from 3 meters of hard drawn BT downlead, coiled around a PVC plumbers pipe of around 25mm diameter and about 30 turns or thereabouts. The actual spec from the dipole centre was as follows:

  • Dipole centre to coil: 3.7 meters
  • Coil to end of dipole leg: 3.3 meters
  • = 7 meters each leg + length of the coil

I replaced the nest was replaced by a half-size G5RV in a “lazy” inverted V configuration, tucked up in the rafters. Good for running a second radio and it gets me on 10m as well as the WARC bands.

Incidentally, when I was testing this original dipole, I started off with 8 meters for each leg and ran it through the MFJ analyser. It was resonant on 6.66 Mhz. An old favorite pirate band that some people may remember. Adding the coils raised the renonant freq from 6.6 to 8.5, so cutting a meter off each side to get the whole thing working for the amateur bands was necessary.

So there you have it, a 45 foot long 40m band dipole.

Pringle Tin Waveguide Antenna 2.4 Ghz project

Not being able to resist the pull of the decibals, I raided the larder tonight for a Pringle tin to build a wave-guide antenna from scrap parts. This is the story of that project.

Manufacture: I soldered a 30.5mm (quarter wave) element to a UHF bulk-head connector and drilled out a hole in the Pringle for hot-glueing. Exactly how far away from the base of the tin I should fit the element took ages – and lots of conflicting web pages. In the end, I aimed for 1/4 wave from the back of the tin. Someone is going to tell me that this is probably the most awful place to stick it – I can believe you 🙂

Pringle Tin Waveguide Antenna 2.4 Ghz

My multimeter couldn’t get a reading on the foil inside the can so I used kid’s water based glue to stick sheets of tin-foil to the outside. This tinfoil was grounded to the base of the tin, although I had some difficuty in doing this because there appears to be some sort of laquor applied to the base. The copper wires seen in the photo were to act as a physical and an electrical assistant; to provide a good ground to the outside of the can.

Ater connecting the Pringle-Wave-Guide to a buffalo wireless access point, I turned it in the general area of the kids room that was running NetStumbler on their network card. I waggled the can around in my shack, and went to the kids room to check if the signal strength had risen at all during the waggling. No luck. So far, it’s as much use as a dummy load.

It just goes to show that some experiments just fail.

Homebrew 3 element yagi for 2.4 Ghz

I needed to get an antenna higher for the kids computer room but a quarter wave vertical didn’t seem to have the gain I wanted, in fact from the kids room I couldn’t even see the network. I hunted for a Pringle can to make a “Can-Tenna” (see https://www.m0mcx.co.uk/?p=17) but apparently we were out of stock(!). A small yagi was the answer:

2.4 Ghz 3 element yagi

I made the driven element directly out of the lossy RG58 coax so that the centre conductor became one side of the driven element and the braid became the other. I used solder to give the wires some strength.

A good test but don’t be fooled. The standard 5/8th antenna shipped with most routers are probably just as good. This yagi needs to be a 5 or maybe 8 element to work better.

I also built a quarter wave last night directly from Westflex W-103, no other components – and although it compared well to the shipped vertical, it only started to match the retail antenna when I gave it some height. Another good (but failed!) experiment!

Coax Loss Comparison

I can never find the comparison charts between RG213 and Henry Westlake’s Westflex W-103. At last, I’ll have this logged forever now. Per 100 meters:

RG213/URM67(Mil spec)
Westflex 103
 100 MHz                      7 dB 5.0 dB
 144 MHz                    8.5 dB ?? dB
 200 MHz                     10 dB 7.5 dB
 300 MHz                     13 dB ?? dB
 400 MHz                     15 dB 11.0 dB
 1000 MHz                   27 dB 18.0 dB

 

Waterproof equipment enclosures

I have just bought some MC to N-type pigtails for the wireless project but now I’m trying to find equipment enclosures to house the router up the mast right next to the grid antenna. Can I find one? Nope. There’s a company paying good money to Google for first place in the rankings for “non metallic enclosure” but the site is so bad(!) and the pages are even named, “NewPage 1” and stuff like that. The MD’s son’s summer project by the look of it. Need to get the pros in!

After much searching, I found a few sources:

AFS 80m SSB Contest

AFS starts soon. I’m here early setting up for it. I can’t hear much, are the bands open? N1MM is working OK but my voice keyer is making nasty noisy QRN from the computer and it’s horrible so I’ve ditched it whilst I consider what to do. This means more fluids (to keep voice in working order!) = more toilet. Last CQWW I used a bucket so I wouldn’t lose my frequency. I’ll just have to cross my legs this time!

I’m logged into the Wythall chat room and waiting for people to join. I love these club activity contests. The anticipation kills me!

         

At 45 minutes before the off, I am holding 3.697 MHz and calling CQ, speaking with MU0FAL (Colin), M3NSQ (Steve in Hornsea), M1EBV (Bristol) and G0ICJ (David from Wythall Club) and I stay on that freq at the off, gradually moving up to 3.698 MHz until 16:21pm with 213 QSOs in the bag. Over the next 100 minutes, I only scored another 45 QSOs, mainly because I lost my frequency through stupidity by deciding I could score more doing some single VFO work, cruising from the bottom of the band through to the top, then I realised what a fabulous frequency I had!

I ran full UK legal power (400 watts) though my FT100Mp Mk5 and my Ameritron 811 amp almost on tickover using a turned-down Class A from the 1000 as the driver for the linear amp. Anyway, finished on 259 which is about 20 QSOs better than last year.

Wythall Chatroom:

15:28:56 [ChrisG1VDP] I am stuck between 2 very loud and wide stations on my running freq…
15:29:24 [g6kmq] m0mcx one of them?
15:45:16 [g0mtn] we’re finished now – time for shopping
15:45:56 [m0mcx] Shopping? Loser
15:46:32 [g0mtn] 133 first hour though. can’t complain
16:50:43 [g7ugc] You swine Chris pinchinf my QSO
16:51:02 [g6kmq] who me?
16:52:21 [g0mtn] back from shopping. now starting cooking… (!)
16:52:26 [g0mtn] scores on the doors so far ?
16:52:44 [g7ugc] 53
16:52:49 [g6kmq] 54
16:52:51 [g0eyo] 54
16:53:24 [ChrisG1VDP] 66
16:54:43 [m0mcx] 234
17:40:54 [m0mcx] Last year: http://www.contesting.co.uk/hfcc/results/2006/afsssb2006.shtml
17:51:23 [g0mtn] remember: fivers to me after the contest
17:54:08 [g0mtn] just received my first log  not even finished yet
17:56:07 [m0mcx] Got called by DL16XXV – sounds like a post code!
18:00:49 [ChrisG1VDP] Do we send the logs to lee to enter the contest?
18:00:58 [g0mtn] yes please.
18:01:24 [g0mtn] i will then send them to myself
18:02:12 [g0mtn] qsy dinner
18:02:53 g0eyo exits from this room
18:03:06 [m0mcx] Me too !

2.4 link signal strength

I have a first class project in tow to put a 2.4GHz link in to the club about 4.5 miles away. I’ve just secured 5 grid dishes with 24dbi of gain for £125. What is a Fresnel zone and how do I spell it?

Anyway, there’s this great site to calculate the potential likelihood of succeeding in putting a link up between one site and another:

ttp://www.atdi.uk.com/WebObjX/default.asp.

It also gives you the dreaded Fresnel Ellipse data which I think I’m slowly starting to understand – essentially, you can block around 40% of the ellipse in one place and the link should still work, but no more. Google it for more.